The present invention relates generally to electrical lamp fixtures used for illuminating aquariums and stimulating the growth of marine life, and specifically to an improved, compact light emitting diode (LED) aquarium light apparatus, incorporating an extended point source LED array (preferably composed of high brightness LEDs of multiple wavelengths) that provides spatially and spectrally controlled light.
Typical aquarium lights utilize either fluorescent bulbs, halogen incandescent bulbs, or metal halide (MH) incandescent bulbs. The primary purpose of most aquarium lights is to provide an attractive illumination of the aquarium tank and its contents, for viewing. In addition, aquarium lights also support the growth of marine life, including marine plants, coral, and potentially algae. The objectives and preferred characteristics of light sources for achieving these two broad purposes can be substantially different, and the different types of light sources used in existing aquarium lights have differing advantages and disadvantages in meeting these objectives.
The preferred characteristics of a light source intended for providing an attractive source of illumination for viewing an aquarium, include a spectral content that is reasonably close to that of natural sunlight, including having a high color rendering index (CRI). The desired spectral content is often intended to reflect the blue shift (or reduction of longer-wavelength red light) that occurs as sunlight passes through water. This results in a natural appearance for fish and other marine life in the aquarium. Some aquarium owners and tropical fish enthusiasts also place value on a light source or lighting system in which the nature of the light can be varied over time, to mimic the differences in sunlight at different times of day, and also to provide light that mimics natural moonlight during the evening.
Another key attribute for aquarium viewing is the spatial distribution of the light from the light source. Light that appears to emanate from a point source, or an approximation of a point source, creates a more natural “shimmering” effect within the aquarium, when the surface of the water is rippled. This effect is created when light emanating from a point source casts shadows of the ripples. This shimmering effect can be observed on the floor or bottom surface of the aquarium, and on the objects within the aquarium. In contrast, a light source that is broadly distributed over the top of the aquarium will result in a blurring of the shimmering effect, with far less contrast. This is similar to the observation that natural sunlight (which emanates from a near point source) creates very sharp and distinct shadows, whereas a distributed light source creates either multiple shadows, or highly-blurred and indistinct shadows. This is because sunlight illuminates an area from only one direction to create distinct shadows, whereas light from a broadly distributed light source will illuminate the area from different directions, thereby causing a blurring of the shadows, or even obliterating the shadows altogether. Existing aquarium light sources that approximate a point source of light, such as a single incandescent bulb, therefore provide an attractive shimmering effect, whereas more distributed light sources, such as a long fluorescent tube, do not provide an attractive shimmering effect.
The preferred characteristics of a light source intended for growing marine life such as marine plants, algae, and coral, are somewhat different from the characteristics that are desired for aquarium viewing. Different types of marine life will prefer different specific wavelengths of light, both in terms of encouraging growth, and also in terms of encouraging specific behaviors and effects. It may also be beneficial to be able to vary the spectral content of the light source over time, either to mimic the day-night cycle, or possibly to mimic longer-term cycles such as the lunar month, as well as seasonal variations that occur in nature. In terms of the light source's spatial distribution, the preferred characteristics include high intensity, as well as uniformity of both the spectral content and intensity over a reasonably large area.
It is also desirable for an aquarium light to have a compact form factor, so that the light does not cover a high percentage of the top of the aquarium tank. An aquarium light with a compact form factor will provide less-obstructed viewing of the aquarium from above, and will also make activities such as feeding, tank cleaning, and other aquarium maintenance tasks, less difficult. Other desirable attributes for a preferred aquarium light include low cost, low electrical power consumption, low or reduced heat generation, high reliability, and long life.
Existing aquarium lights and aquarium light source technologies have different advantages and disadvantages, for the dual purposes of providing an attractive source of illumination for aquarium viewing, and encouraging the growth of marine life. Fluorescent bulbs, as well as incandescent bulbs, such as halogen and metal halide light sources, provide a fairly broad spectrum of light, and can provide good or at least acceptable color rendering. However, their spectral content is fixed. Thus, varying the spectral content over time is not possible, unless multiple bulb types are incorporated into the light. It is also not possible to tailor the spectral content to emphasize the specific wavelengths that might be optimal for the growth of marine life. It is also true that incandescent bulbs in particular (and fluorescent bulbs to a lesser extent) may produce significant quantities of radiated infrared energy, which serves to heat the water in the aquarium. This may require a cooling apparatus for the water in the aquarium tank, which in turn adds to the energy, costs of the aquarium.
In terms of spatial distribution, incandescent bulbs can be configured to approximate a point source, and therefore can provide an attractive shimmering effect. However, fluorescent bulbs typically provide a more distributed light pattern, and do not provide attractive shimmering. As a result of these differences in characteristics, some aquarium light fixtures incorporate both incandescent and fluorescent bulbs, to be used at different times for differing purposes. As just one example, the incandescent bulb(s) might be used for simulating daylight (perhaps in combination with fluorescent bulbs), whereas a dimmer fluorescent bulb might be used to simulate moonlight.
Aquarium lights using Light Emitting Diodes offer a number of potential advantages over fluorescent or incandescent bulbs. Many of these general advantages are described in prior art patent U.S. Pat. No. 7,220,018 B2, “MARINE LED LIGHTING SYSTEM AND METHOD.” First and foremost of the general advantages of LED aquarium lights is that individual LEDs emit light over a narrow range of wavelengths. By combining multiple LEDs of specific wavelengths, it is possible to tailor the overall spectral content of the light source, for either a particular visual appearance, or for encouraging the growth of marine life. If the control electronics for the LED aquarium light are designed so that the brightness of different wavelength LEDs is separately controllable, then it is also possible to vary the spectral content of the overall LED light source as a function of time, to mimic the day-night cycle, or even the changes that occur in natural sunlight as a function of time-of-day. Since LED chips only emit light from their top surfaces, LED-based light sources tend to require simpler reflectors than incandescent or fluorescent bulbs. Other general benefits of LED aquarium lights include high efficiency, especially when compared to incandescent bulbs, as well as the lack of radiated IR energy that could excessively heat the water in the aquarium.
However, existing LED aquarium lights also suffer from several important disadvantages. The primary historical disadvantage of existing and prior art LED lights in general has been their relative lack of total light output, compared to fluorescent and incandescent light sources. Research in LEDs and solid-state lighting has resulted in the development of high brightness LEDs that efficiently produce relatively larger levels of light output, at higher electrical current levels. This has largely been achieved via advances in drawing heat away from the active junction of the LED, thereby allowing the LED to safely operate at these higher current levels. The electrical-to-optical conversion efficiency of LEDs is also being improved over time.
However, in order to provide a sufficient total light output, prior art LED aquarium lights require relatively large numbers of LEDs, which are typically spaced widely apart in order to deal with the resultant heat dissipation issues. The spacing between adjacent LEDs or LED chips in prior art LED aquarium lights is therefore an inch or more, and is typically several inches. This negates much of the potential size and cost advantages of an LED aquarium light. In order to achieve the light output of 20 or more LED chips, the surface area of the prior-art LED aquarium light must be relatively large. Also, each of the widely-spaced LED chips requires individual separate packaging, separate heat-sinking, and separate optics, thereby adding significantly to the size and cost of the aquarium light.
Typical practice in existing LED aquarium lights is to distribute a large number of individually-packaged LEDs along the length and width of a “light panel”, or alternatively, along the length of a “light bar”. This creates a highly distributed spatial light pattern, similar to that provided by the use of one or more long fluorescent tubes. This highly distributed light pattern blurs the shadows and does not provide the attractive shimmering visual effect that would result from a point source of light. Also, if multiple wavelengths of LEDs are being used to achieve a desirable spectral profile, the different wavelengths will be positioned at different locations along the light panel or light bar. This results in poor mixing of the light of different wavelengths from the spatially separated LEDs, causing different areas of the aquarium tank to receive light with differing spectral content. The large size of LED light panels and light bars also covers up a large portion of the top surface of the aquarium, blocking viewing of the aquarium from above, and blocking access for aquarium maintenance and other tasks.